The primary role of sodium in ion transport and the central importance of calcium in membrane processes make the interaction of these ions in transport mechanisms worthy of study. This project will concern the interdependence of these cations in transepithelial movement and the effect of certain drugs and hormones thereon, as well as some possible applications in pharmacological control of sodium and calcium metabolism. By correlating measurements of net transport with studies of cell morphology and of the intracellular content and distribution of these cations and of selected enzymes, we hope to shed light on the cellular mechanisms of ion transport and their regulation.